#105: Ensure guile mode active when calling callbacks/functions

Since some GLib primitives can spawn new threads, we
need to ensure that Guile is active whenever
scheme callbacks and functions are called.

* src/gig_callback.c (callback_binding): init guile
* src/gig_function.c (function_binding): init guile

src/gig_callback.c

@@ -180,6 +180,10 @@ callback_binding(ffi_cif *cif, gpointer ret, gpointer *ffi_args, gpointer user_d
     SCM s_args = SCM_EOL;
     SCM s_ret;
 
+    // When using GLib thread functions, this could be the entrypoint
+    // into Guile for this thread.
+    scm_init_guile();
+
     g_assert(cif != NULL);
     g_assert(ret != NULL);
     g_assert(ffi_args != NULL);

src/gig_function.c

@@ -1,4 +1,4 @@
-// Copyright (C) 2018, 2019, 2020 Michael L. Gran
+// Copyright (C) 2018, 2019, 2020, 2021 Michael L. Gran
 
 // This program is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
@@ -626,6 +626,10 @@ function_binding(ffi_cif *cif, gpointer ret, gpointer *ffi_args, gpointer user_d
     GObject *self = NULL;
     SCM s_args = SCM_UNDEFINED;
 
+    // When using GLib thread functions, could this be the entrypoint
+    // into Guile for this thread?
+    scm_init_guile();
+
     g_assert(cif != NULL);
     g_assert(ret != NULL);
     g_assert(ffi_args != NULL);